Network terminal apparatus, communication overload avoiding method and program

ABSTRACT

A network terminal apparatus of the present invention includes an overload condition detecting unit detecting communication overload condition and an overload condition completion detecting unit detecting recovery from an overload condition, invalidates data received by LAN chip when an overload condition is detected, and releases said invalidation when recovery from an overload condition is detected.

TECHNICAL FIELD

The present invention relates to a network terminal apparatuseliminating negative impact caused by communication overload condition,and particularly to a network terminal apparatus processing video dataat home.

BACKGROUND ART

In general, a communication overload condition of a network terminalapparatus connected to the IP network causes excessive communicationprocessing load on the IP layer and the lower layers of a networkterminal apparatus, resulting in significant occupancy of CPU processingcapability by communication processing, which impacts negatively notonly on communication processing but also on the other processing.

Also a Denial of Service attack (DoS attack) can be considered as one ofthe causes of overload communication condition. An example of atechnique to prevent communication overload caused by such DoS attack isthe illicit access defense system described in Japanese Laid-Open Patentapplication No. 2002-158660 publication. As shown in FIG. 8, the systemis configured to filter Internet Protocol (IP) packets at attacker'srouters (Attack breaker 100 and 200), in a case where CommunicationControl Device 3 notices a direction of communication control to theattacker's network according to a judgment by a network administratorwhen a DoS attack is detected by an Attack Detection Device 2, in theconfiguration. This configuration enables to prevent communicationoverload condition.

However, the above-mentioned conventional technique requires thejudgment by a network administrator possessing specialized knowledge andalso additional devices equipping a filtering function to attacker'snetwork, which makes it difficult to apply to home consumer networkapparatuses.

Furthermore, when the CPU of the network apparatus processing video datais occupied by communication processing due to communication processingoverload, negative impact delaying the major processing (video dataprocessing and so on) other than communication processing occurs, and auser may misunderstand the condition as a failure. Especially, sincevideo data processing requires real-time processing, negative impactcaused by communication overload condition must be completelyeliminated.

An object of the present invention is to provide a network terminalapparatus that enables smooth processing of the main apparatus whichincludes the network terminal, preventing communication overloadcondition without user's judgment or external additional devices.

DISCLOSURE OF INVENTION

In order to achieve the above-mentioned object, a network terminalapparatus of the present invention includes a communication unit tocommunicate through a network, a judgment unit to judge whether or notthe communication is in an overload condition and an invalidation unitto invalidate data received by the communication unit in the case wherethe judgment is that the communication is in an overload condition.

With this configuration, the received data is invalidated under anoverload condition. Therefore, the negative impact to the communicationprocessing and the other processing can be eliminated even under acommunication overload condition without user's judgment or additionaldevices. In fact, the receiving processing does not occupy theprocessing capability of the CPU, and it is possible to continue theother processing without degrading the quality. Therefore, the presentinvention is readily applicable to the network terminal apparatus usedat home and other processing can be executed smoothly. For instance, asanother processing other than communication processing, even the networkterminal apparatus executing video data processing requiring real-timeprocessing can eliminate the negative impact caused by a communicationoverload condition. Actually, in the case where the judgment is that thecommunication is in an overload condition, the received data is blockedlike a circuit breaker without checking the types or the contents of thereceived data, hence the processing in the network terminal apparatuscan be protected by a simple configuration which does not require user'ssetting.

Under this configuration, the judgment unit may be configured to judgethat the communication is in an overload condition in the case where anamount of data received per unit time from the network exceeds athreshold.

The judgment unit may be also configured to judge that the communicationis in an overload condition in the case where an amount of data receivedin a receiving buffer that temporarily holds the received data exceedsthe threshold.

With this configuration, the overload condition can be judgedimmediately using the threshold for an amount of the received data.

The judgment unit may be also configured to judge the received data incommunication processing corresponding to the data link layer using thethreshold.

With this configuration, the threshold judgment is carried out on thelevel of the data link layer, therefore the network layer and the upperlayers are not negatively impacted by load caused by threshold judgment.

Furthermore, the network terminal apparatus may be configured to equip adetermination unit to dynamically determine the threshold depending on aload condition of a processing other than the communication processingin the network terminal apparatus, and the judgment unit judges whetheror not the communication is in an overload condition using thedetermined threshold.

With this configuration, the threshold is dynamically determined,therefore the communication overload condition can be changeddynamically depending on the size of a load of a processing other thanthe communication processing in the network terminal apparatus.Accordingly, the negative impact to processing requiring real-timeprocessing other than the communication processing in the networkterminal apparatus can be eliminated, and processing capabilities of thewhole network terminal apparatus can be maximized.

Additionally, the determination unit may be configured to determine thethreshold depending on the number of running application programs in thenetwork terminal apparatus.

The determination unit may be also configured to determine the thresholddepending on (i) the number of running application programs in thenetwork terminal apparatus and (ii) a weight predetermined with respectto each application program.

With the configuration, the dynamic threshold determination can bereadily carried out depending upon the number of running applicationprograms. Moreover, a weighting to the number of each applicationprogram enables to set up an appropriate threshold depending on a loadof a processing of the running application.

The communication unit includes a first communication processing unit toexecute a communication processing corresponding to the physical layerand the data link layer, a receiving buffer to temporarily hold receiveddata from the first communication processing unit and a secondcommunication processing unit to take the received data from thereceiving buffer and execute communication processing corresponding tothe network layer and the upper layers. The judgment unit may beconfigured to judge the communication to be in an overload condition inthe case where an amount of the received data in the receiving bufferexceeds the threshold.

With the configuration, an overload condition is detected bycommunication processing in the second communication processing unit(e.g. IP processing).

The communication unit may be configured to execute hierarchicalcommunication processing and the invalidation unit prohibits one of theinterlayer logical connection.

With this configuration, the load on the communication processing layer,which locates above the layers where connection being prohibited, iseliminated and the processing load on the processing in the networkterminal apparatus other than communication processing is eliminated aswell. Hence, the processing other than communication processing are notnegatively impacted under a communication overload condition.

The invalidation unit may be configured to prohibit the firstcommunication processing unit from notifying the second communicationprocessing unit of received data.

With the configuration, the invalidation unit enables to eliminate theload of communication processing in the network layer and the upperlayers under a communication overload condition just by prohibiting thenotification of the received data. When the processing in the secondcommunication processing unit is realized by software and the CPU, theload of communication processing to the CPU can be eliminated.

The network terminal apparatus in the present invention may also beconfigured to equip the communication unit to communicate through anetwork, a first detection unit to detect that the communication is inan overload condition, an invalidation unit to invalidate data receivedby the communication unit in the case where an overload condition isdetected, a second detection unit to detect a recovery from the overloadcondition, and a release unit to release the invalidation by theinvalidation unit when a recovery from the overload condition isdetected.

In addition, a communication overload condition avoiding method in thepresent invention and its program have the same unit with theabove-mentioned network terminal apparatus, and the same functions andeffects are secured.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a major hardware configuration of a network terminalapparatus (a communication overload condition avoiding apparatus) in theembodiment of the present invention.

FIG. 2 is a block diagram showing the functions of major units of thecommunication overload condition avoiding apparatus.

FIG. 3 is a flowchart showing a detailed example of communicationoverload condition detection processing performed in the overloadcondition detecting unit.

FIG. 4 is a flow chart showing a detailed example of how the overloadcondition completion detecting unit detects the completion of anoverload condition.

FIG. 5 is a table showing correspondence between the number ofapplications being executed and respective thresholds.

FIG. 6A is a table showing correspondence between applications and therespectively corresponding weighting values.

FIG. 6B is a table showing other correspondences between applicationsand the respectively corresponding weighting values.

FIG. 7 shows a system example including a home appliance applying acommunication overload condition avoiding apparatus.

FIG. 8 shows the configuration of an illicit access defense system in aconventional technique.

BEST MODE FOR CARRYING OUT THE INVENTION

[Hardware Configuration of a Communication Overload Condition AvoidingApparatus]

FIG. 1 shows a major hardware configuration of a network terminalapparatus in the embodiment of the present invention. This networkterminal apparatus is called communication overload condition avoidingapparatus 10 in the figure, includes a Central Processing Unit (CPU) 11,a memory 12, an interrupt controller 13, a LAN chip 14 and a LAN I/F(interface) 15 and communicates with a communication host 16 and so onthrough the Internet Protocol (IP) network 17.

This hardware configuration is a general configuration and the memory12, having an area as a receiving buffer used temporarily for storingdata received, stores a program describing communication overloadcondition avoiding method in the present invention. The CPU 11 judgeswhether or not the condition being in communication overload byexecuting this program. The communication overload condition avoidingapparatus 10 is configured so that it can cancel the data received whenthe CPU 11 judges the condition as overload. The communication overloadcondition herein means a state that processing (for example, video dataprocessing requiring real-time processing) other than communication inthe communication overload condition avoiding apparatus 10 are notexecuted properly.

Firstly, the operations performed by the hardware at the time ofreceiving data under communication non-overload condition (hereafter,called steady state) will now be explained.

LAN chip 14 is, for example, a controller, which conforms to theInstitute of Electrical and Electronic Engineers (IEEE) 802.3 standard(called as Ethernet (R)), executing communication processing of datalink layer and a part of physical layer. When the LAN chip 14 receives aframe (called as Ethernet (R) frame) to its own address through the LANI/F 15, the LAN chip 14 notifies the interrupt controller 13 of the factaccordingly. When the interrupt controller 13 received this notice, theinterrupt controller 13 causes reception interrupt to the CPU 11further. The reception interrupt is an interrupt notifying the presenceof data received.

After receiving the reception interrupt, the CPU 11 reads the datareceived by the LAN chip 14 out of the buffer in the LAN chip 14 andtransfers to the memory 12, followed by IP processing. On this occasion,under a steady state, the CPU 11 executes detection processing ofcommunication overload condition by checking the amount of data receivedper unit time by executing a program in the memory 12.

Secondly, operation in hardware at the time of detecting, avoiding andrecovering from a communication overload condition (hereafter, alsocalled unsteady state) will now be explained.

Assuming that the communication host 16 starts a large amount ofcommunication to the network terminal apparatus 10. When the CPU 11detects a communication overload condition, masks interrupt signal fromthe LAN chip 14 to the interrupt controller 13. This eliminates theoccurrence of reception interrupt of Ethernet (R) to the CPU 11 andcommunication overload condition can be avoided.

In an unsteady state, the CPU 11 executes processing of detectingcompletion of an overloaded condition by executing a program in thememory 12, and cancels the above-mentioned interrupt mask to theinterrupt controller 13 upon detecting the completion of an overloadcondition. Accordingly, this realizes a recovery from unsteady state tosteady state. This hereinbefore explained is the outline of theoperation in hardware.

[Functional Configuration of the Communication Overload ConditionAvoiding Apparatus]

FIG. 2 is a block diagram showing the functions of major units of thecommunication overload condition avoiding apparatus 10 shown in FIG. 1.The communication overload condition avoiding apparatus 10 includes aLAN chip 14, a LAN I/F 15, a network driver 23, an Internet Protocol(IP) processing unit 24, an overload condition detecting unit 25 and anoverload condition completion detecting unit 26. The numbers of eachunit are matched to the same unit in FIG. 1.

The LAN chip 14 executes communication processing in both the PHY layer21 corresponding to a part of the physical layer and the MAC layer 22corresponding to a part of the data link layer in the Open SystemInterconnection (OSI) reference model.

The LAN I/F 15, as processing for a part of the physical layer,functions to conform a frame to be communicated between the LAN chip 14and the IP network to the electrical specification of the LAN chip 14.

The network driver 23, in a steady state, executes communicationprocessing for a part of the data link layer. This communicationprocessing is usual processing as a device driver, and includes datatransmission from the LAN chip 14 to the memory 12 executed in responseto reception interrupt explained in FIG. 1. The network driver 23 is, inan unsteady state, substantially prohibited from executing processingbecause an interrupt signal is masked.

The IP processing unit 24, in a steady state, executes IP processing onthe data received by and sent from the network driver 23.

The overload condition detecting unit 25, in a steady state, judges thestate being in communication overload condition when the amount of thedata received per unit time exceeds a threshold, and then masks aninterrupt signal being transmitted from the interrupt controller 13 tothe CPU 11.

The overload condition completion detecting unit 26, in an unsteadystate, executes polling processing to check the presence of receivedframes in a buffer of the LAN chip 14. When the state where the receivedframe is not present continues for a predetermined period, the overloadcondition completion detecting unit 26 judges overload condition beingcompleted and releases the above-mentioned interrupt mask to theinterrupt controller 13.

The above-mentioned overload condition detecting unit 25 executes ameasurement and carries out the threshold judgment by the result of themeasurement. With respect to specific methods by the overload conditiondetecting unit 25 for judging whether or not the data received per unittime exceeds a threshold, the result of the measurement such as theamount of the data received (e.g. the number of bits, bytes, frames, IPpackets and so on) for a predetermined duration (e.g. 10 ms), or theduration required for receiving the fixed amount of data (e.g. thenumber of any of bits, bytes, frames or IP packets) may be used.

[A Detailed Flow of Communication Overload Condition DetectingProcessing]

The example of the threshold judgment by a measurement result of theduration required for receiving a fixed amount (the number of frames: W)of data received, which is one of the specific example for judgingwhether or not the data received per unit time exceeds the thresholdperformed by the overload condition detecting unit 25, will now beexplained.

FIG. 3 is a flowchart showing a detailed example of communicationoverload condition detection processing performed by the overloadcondition detecting unit 25. S300 to S302 and S309 in the flowchart arenot involved in the communication overload condition detectingprocessing performed by the overload condition detecting unit 25, butS300 to S302 show the processing until the step of activatingcommunication overload condition detecting processing by receptioninterrupt in FIG. 1 and S309 shows the communication processing by thenetwork driver 23 respectively.

A frame counter in the figure functions to count W of frames and carriesout countdown from W to zero. A time stamp Tn, a resister, functions tohold time obtaining from a real-time clock in the communication overloadcondition avoiding apparatus 10, and shows the time when the currentframe is received. A time stamp Tn-1, a resister, functions to hold thereceiving time of the frame W before the current frame. Tn-Tn-1expresses the duration of the interval required to receive W of frames.Threshold A is an indication used to judge whether or not the interval(Tn-Tn-1) is too short (in an overload condition). The threshold A isset up not to impact negatively on other processing in the communicationoverload condition avoiding apparatus 10 by communication processing.Additionally, the default value for the frame counter, the time stamp Tnand the time stamp Tn-1 are all zero.

When the LAN chip 14, in a steady state, receives a frame (S300) throughthe LAN I/F 15, the LAN chip 14 causes a reception interrupt (S301) byway of the interrupt controller 13. The CPU 11 received this factsubsequently activates the overload condition detecting unit 25 bycalling a program corresponding to the overload condition detecting unit25 (S302).

Processing afterward are individually explained in two different casesi.e. in the case of initial frame reception and in the case of a secondtime thereafter.

In the case of initial frame reception, the overload condition detectingunit 25, as the frame counter showing zero (S306), assigns the value ofthe time stamp Tn to Tn-1 (S305) and obtains the current time from thereal time clock as a value for the time stamp Tn (S306), then sets up astart-up value W to the frame counter (S307). According to this, as apreparation for receptions from the second time thereafter, the timestamp Tn is updated to the current frame reception time and the value ofthe frame counter is updated to W respectively. The value of Tn-1remains zero. Moreover, since (Tn-Tn-1) exceeds the threshold A (S308),the overload condition detecting unit 25 activates the network driver 23and causes it to execute reception processing (S309).

In the case of the second time thereafter for frame receptions, unlessthe frame counter shows zero, in other words, unless the overloadcondition detecting unit 25 has not received W of frames (S303: false),the overload condition detecting unit 25 decrements the frame counter(S304) and activates the network driver 23 to make it execute receptionprocessing (S309).

On the other hand, when the frame counter shows zero, in other words,when the overload condition detecting unit 25 has received W of frames(S303: true), the overload condition detecting unit 25 assigns a valueof the time stamp Tn to Tn-1 (S305). According to this, the time stampTn-1 shows the reception time of the frame, which is W frames before.Furthermore, the overload condition detecting overload conditiondetecting unit 25 obtains the current time from the real time clock, andsets up the value of the time stamp to Tn as the current frame receivedtime. When a duration of the interval (Tn-Tn-1) is less than thethreshold A (S308: true), the overload condition detecting unit 25 masksan interrupt signal of the interrupt controller 13 (S310), andsubsequently notifies a detection of communication overload condition tothe CPU 11 (S311), then activates the overload condition completiondetecting unit 26 (S312).

The interrupt mask blocks the notification of an interrupt being sentfrom the interrupt controller 13 to the CPU 11. Afterward, hardwareinterrupt processing related to LAN communication does not occur and thenetwork driver 23 and the overload condition detecting overloadcondition detecting unit 25 are not activated. Alternatively, a task ofcommunication overload condition completion detecting processing isexecuted.

On the other hand, when the duration of the interval (Tn-Tn-1) is notless than the threshold A (S308: false), which is not overloadcondition, the overload condition detecting unit 25 activates thenetwork driver 23 to make it execute the reception processing (S309).

[Threshold Example]

The above-mentioned threshold A may be set up (initial value W of framecounter, threshold A) as (85 frames, 10 ms) or (170 frames, 20 ms) inthe case where the LAN transmission speed is 100 Mbps, although itdepends on the capacity of the CPU 11. And also (8 frames, 10 ms) or (17frames, 20 ms) may be set up in case of 10 Mbps. The set-up value of thethreshold A should be sufficiently longer duration than the maximum timeof typical burst frame reception.

The aforementioned threshold value A can be dynamically determineddepending upon the condition of processing load other than thecommunication in the communication overload condition avoiding apparatus10. In that case, the threshold A may be determined in the step betweenS307 and S308 in FIG. 3. In this threshold determination step, theoverload condition detecting unit 25, for example, determines thethreshold corresponding to the number of running applications as thethreshold A for the judgment by predetermining multiple thresholds A1,A2 . . . to be corresponded to the number of running applications L bythe CPU 11 as shown in FIG. 5.

This dynamic threshold determination enables dynamic change of thethroughput where communication processing can occupy the processingcapacity in the CPU 11, and the dynamic definition of communicationoverload condition depends on the processing load is heavy or lightother than communication processing in the communication overloadcondition avoiding apparatus 10. Therefore, negative impact onprocessing requiring real-time processing other than communicationprocessing in the communication overload condition avoiding apparatus 10can be eliminated, moreover the processing capability of the wholecommunication overload condition avoiding apparatus 10 can be maximized.

Additionally, the threshold may be determined by means of weightingapplications, besides determining by corresponding the thresholds to thenumber of running applications as explained in the above-mentionedthreshold determination step. And more specifically, with regard to theapplications with large amount of processing and applications requiringreal-time processing, the overload condition detecting unit 25 convertsthe number of applications from one to weighted number such as two,three and so on, sums up the total number of applications and determinesthe corresponding threshold. FIG. 6A shows converted values to therespective applications. In the figure, the number of applications forApp1, 4, 5 and so on remain one, while the number of applications forApp2 is converted to two and the number of applications for App3 isconverted to three likewise. This enables to absorb the difference ofprocessing volume for each application and dynamically determine moreappropriate thresholds. FIG. 6B shows an example of other convertedvalues. In this example, the number of applications of App1 is convertedto five. For instance the threshold value decreases during application 1being running so that the processing of application 1 can be protectedwithout delay due to data receiving processing.

[Detailed Example of Overload Condition Completion Detecting Processing]

When the overload condition detecting unit 25 detects an overloadcondition, the overload condition completion detecting unit 26 isactivated and executes processing to detect overload conditioncompletion.

FIG. 4 is a flow chart showing a detailed example of how the overloadcondition completion detecting unit 26 detects the completion of anoverload condition. In the figure, loop 1 is a loop processing ofcontinuous repetition for a predetermined duration (e.g. 10 ms) and loop2 is a loop processing performed one time for predetermined duration(e.g. 5 seconds). More specifically, the overload condition completiondetecting unit 26 performs loop 1 processing of 10 ms every 5 seconds aspolling processing. Also N is the value from a counter for counting upfrom zero to five and the value represents the number of times judgedcommunication overload condition to be solved with high possibility.

At first, the overload condition completion detecting unit 26initializes the value of the counter to N=0 (S400). And then, theoverload condition completion detecting unit 26, as a loop 1 processing,checks whether any data received is being held in the buffer of the LANchip 14 (S403). When any data is being held, the overload conditioncompletion detecting unit 26 reads the data received (S404), and thencounts the number of frames m composed of the data received. Thisrepetition is performed for 10 ms continuously as the loop 1. As aresult of this, the number of received frames m is counted for 10 ms.

After the end of the loop 1, the overload condition completion detectingunit 26 judges whether or not the number of received frames m is lessthan a threshold B (S407). When the number of received frames m is lessthan the threshold B, N is incremented (N=N+1) (S408) and when thenumber of received frames m is not less than the threshold B, N iscleared (N=0) (S409). When the number of received frames m is less thanthe threshold B, it is regarded as the communication overload conditionbeing eliminated with high possibility. The threshold B, for instance,may be set to 85 in the case of transmission speed being 100 Mbps and to8 in the case of 10 Mbps. The same value as the above-mentionedthreshold A may be used, or the value being set dynamically likethreshold A shown in FIG. 4 and FIG. 5 may be used as well.

Moreover, the overload condition completion detecting unit 26 judgeswhether or not N is not less than 5 (S410). In this judgment when theresult of loop 1 indicating that an overload condition has beeneliminated with high possibility is recognized five straight times, thecompletion of a communication overload condition is judged.

When the N is judged to be less than 5, the overload condition detectingunit 25 performs one time of the loop 2 processing again after 5seconds. When the N is judged to be not less than 5, the interrupt maskis released to the interrupt controller 13 (S412), and overloadcondition completion is notified to the CPU 11 (S413) then theprocessing is completed.

According to this, the interrupt mask is released and the condition isrecovered from an unsteady state to a steady state.

[System Example]

An embodiment where network terminal apparatus (the communicationoverload condition avoiding apparatus 10) shown in FIG. 1 and FIG. 2 isapplied to a home appliance will now be explained.

FIG. 7 shows a system example including a home appliance applying acommunication overload condition avoiding apparatus 10. In the system ofthe figure, a set-top box (STB) 10 a, a DVD recorder 10 b, a home server10 c, a personal computer (PC) 103 and also a network I/F (interface)104 are all connected to LAN, and further connected to a distributionserver 105 on the internet through the network I/F (interface) 104.

Among them, the STB 10 a, the DVD recorder 10 b and the home server 10 chave the configuration of the communication overload condition avoidingapparatus 10 shown in FIG. 1 and FIG. 2 respectively.

The STB 10 a performs (1) processing to receive the streaming data sentfrom digital broadcasting, (2) processing to receive the streaming datasent from one of the home server 10 c, the distribution server 105 andso on through LAN, (3) processing to reproduce the streaming data andoutput the reproduced data to the television 102, (4) processing to sendthe streaming data on LAN, and so on. Each of processing (1) to (4) allrequire real-time processing, but (1) and (3) require real-timeprocessing more strictly, while (2) and (4) may be performed in realtime by re-transmitting.

For example, the streaming data received in (1) is played in (3), whilethe streaming data received in (2) is displayed in reduced size on thetelevision 102 in (3).

In this example, a communication overload condition is assumed to becaused by unusually large amount of the data received in (2) or byimproper transmission of frames addressed to the STB 10 a for somereason. The STB 10 a avoids an overload condition by stopping thereceiving processing in (2) by means of an interrupt mask on detectingan overload condition. According to this, the processing in (1) and (3)are smoothly performed without delaying reproduction processing ordropping any frame caused by an overload condition.

Also, since the STB 10 a is detecting overload condition completionwhile avoiding overload condition, the condition returns to the originalcondition after the overload condition being eliminated.

The DVD recorder 10 b performs processing chiefly such as (a) processingto receive television broadcasting, (b) processing to receive thestreaming data transmitted from the home server 10 c or the distributionserver 105 through LAN, (c) reproduction the streaming data orprocessing to output the reproduced data to the television 102, (d)processing to transmit the streaming data to LAN and (e) processing torecord DVD. The processing (a) to (d) are approximately the same asaforesaid (1) to (4), while the processing of the DVD recorder 10 b ismore complex and large volume in terms of performing recordingprocessing (e).

For instance, the video data available from the STB 10 a or a built-intuner (not shown in the figure) is assumed to be under the processing ofrecording (e) and reproducing in (c) the received streaming data in (b).Real-time processing is required for the recording processing (e) andreproduction processing from (b) to (c) as well, especially recordingprocessing (e) requires real-time processing more strictly.

In this case, detecting, avoiding and recovering from overload conditionare executed like above-mentioned STB 10 a in the case of acommunication overload condition.

The home server 10 c stores the streaming data and files in the built-inhard disk and sending and receiving the streaming data or files to andfrom other apparatuses through LAN. Detecting, avoiding and recoveringfrom overload condition are same as the STB 10 a and DVD recorder 10 b.

The STB 10 a, the DVD recorder 10 b and the home server 10 c equippingthe communication overload condition avoiding apparatus 10 insiderespectively are capable of detecting, avoiding and recovering fromoverload condition by the apparatus alone without external additionaldevices or user's judgment as shown above.

As explained hereinbefore, since the network terminal apparatus in thepresent invention invalidates the received data under overloadcondition, it is possible that elimination of the impact tocommunication processing and other processing under communicationoverload condition without user's judgment or additional apparatus. Itmeans that the receiving processing does not occupy the processingcapability of the CPU, hence it is possible to continue withoutdegrading the quality of the other processing. Therefore, this isreadily applicable to the network terminal apparatus used at home andother processing can be executed smoothly. For instance, as a processingother than communication processing, even the network terminal apparatusexecuting video data processing requiring real-time processing caneliminate the impact caused by a communication overload condition.

The router used as the network I/F 104 normally blocks an arbitrarysender's address or a protocol set by user and may function to filter toregulate the flow. However this user setting needs a troublesomeoperation and specialized knowledge. The configuration in the FIG. 7enables detecting, avoiding and recovering from an overload conditioncorresponding to flow regulation without any troublesome user'soperation.

By contraries, when user sets filtering function, the assigning and thesupplementing the functions are enabled by the combination of thefiltering function by the network I/F 104 and the individual functionsof detecting, avoiding and recovering from overload condition of the STB10 a, the DVD recorder 10 b and the home server 10 c. The configurationmay be arranged as the STB 10 a, the DVD recorder 10 b and the homeserver 10 c individually enable and disable the functions of detecting,avoiding and recovering from an overload condition in this case.

The same effect can be expected by arranging the configuration ascombining two of the arbitrary apparatuses or three of the apparatusesof the STB 10 a, the DVD recorder 10 b and the home server 10 c in FIG.7 by equipping the communication overload condition avoiding apparatus10. It is also possible to equip the communication overload conditionavoiding apparatus 10 to the personal computer 103.

The overload condition detecting unit 25 measures the amount of the datareceived reached to the data link layer (LAN chip 14) per unit time, butthe measurement result of the amount of the data received reached to thenetwork layer (the IP processing unit 24) per unit time may also be usedfor the threshold judgment in the configuration. In this case, theoverload condition detecting unit 25 can judge whether or not thereceiving processing in the network layer (the IP processing unit 24)overflowed, instead of making threshold judgment by measuring the amountof the receiving data reached to the network layer (the IP processingunit 24) per unit time.

Additionally, the overload condition detecting unit 25 may measure theamount of the receiving data in the receiving buffer (in the area of thememory 12), which holding the data received transmitted from the LANchip 14 temporarily and use the measurement result for the thresholdjudgment, instead of measuring the amount of the receiving data reachedto the data link layer (the LAN chip 14) per unit time.

In the above-mentioned embodiment, the overload condition detecting unit25 prohibits the notification of the receiving data from the data linklayer (the LAN chip 14) to the network layer (the IP processing unit 24)by masking the interrupt signal. Alternatively, it may be configuredthat the notification of the receiving data or the transmission of thereceiving data between the different layers in a communication hierarchyis prohibited. For instance, it may be configured (A) to prohibit thetransmission of the receiving data from the physical layer (LAN I/F 15)to the data link layer, or (B) to disable operations any of the physicallayer, the data link layer and the network layer.

And also, in the system example in FIG. 7, it may be configured that theoverload condition detecting unit 25 notifies an overload condition tothe network I/F 104, and the packet addressed to the communicationoverload condition avoiding apparatus 10 is abandoned (or be filtered)in the network I/F 104, instead of masking the interrupt signal by theoverload condition detecting unit 25. In this case, it may be configuredthat when the network I/F 104 is notified the overload condition, thepackets addressed to the communication overload condition avoidingapparatus 10 to be abandoned. The network I/F 104 can determine whetheror not the packet being addressed to the communication overloadcondition avoiding apparatus 10, using, for example, the IP address orthe port number of the receiver. In this case the network I/F 104further equipping the overload condition completion detecting unit 26and it may be configured that filtering of the packets is stopped whenan overload condition completion is detected by the overload conditioncompletion detecting unit 26.

In this configuration, the packets addressed to the communicationoverload condition avoiding apparatus 10 are abandoned by the networkI/F 104 during all the time of communication overload condition of thecommunication overload condition avoiding apparatus 10. Therefore theapparatuses equipping the communication overload condition avoidingapparatus 10 (e.g. the STB 10 a, the DVD recorder 10 b and so on) cansmoothly execute the primary processing other than communicationprocessing without negative impacts such as processing delay.

Additionally, in the embodiment above, the communication overloadcondition avoiding apparatus 10 may be equipped with notification unitnotifying the user of communication overload condition by means ofsound, light, indication and so on under communication overloadcondition. For example, on the STB 10 a and the DVD recorder 10 b inFIG. 7, the above-mentioned notification unit may function to indicatethe superimposed notification such as “The reception is limited for awhile due to a communication overload condition”, “The reception isbeing limited due to a communication overload condition” and “Recoveredfrom communication overload condition” and so on to the video signal tothe television 102 at the each timing of detecting, avoiding andrecovering from the communication overload condition.

In the embodiment above, the communication processing on the data linklayer is realized by the network driver 23 and the CPU 11, but theparticular LSI chip can be used instead of the CPU 11. And also thecommunication processing (the Internet Protocol processing unit 24) onthe network layer is realized by the CPU 11 on the software, but theparticular LSI chip can be used instead.

The correspondence between the number of running applications and thethresholds shown in FIG. 5 may be configured to be changeable by remotemaintenance from an external apparatus or be changeable by the usersetting. In case of the change by the user setting, it may be configuredto be selected by users preparing multiple corresponding tables in thenetwork terminal apparatus.

INDUSTRIAL APPLICABILITY

The present invention is suitable for the network terminal apparatusesto be connected to the network to execute data communication, especiallyas a network terminal apparatus to be connected to LAN and so on athome, for instance, the network terminal apparatuses such as a Set-TopBox (STB) for receiving digital broadcasting, a digital TV, a DigitalVersatile Disc (DVD) recorder, a Hard Disk Drive (HDD) and so on forcontents recording and reproduction apparatuses and also the complexequipment of these apparatuses are suitable.

1. A network terminal apparatus, comprising: a communication unitoperable to communicate through a network; a judgment unit operable tojudge whether or not the communication is in an overload condition; andan invalidation unit operable to invalidate data received by saidcommunication unit in the case where said judgment unit judges that thecommunication is in an overload condition.
 2. The network terminalapparatus according to claim 1, wherein said judgment unit is operableto judge the communication is in an overload condition in the case wherean amount of data received per unit time from the network exceeds athreshold.
 3. The network terminal apparatus according to claim 1,wherein said judgment unit is operable to judge the communication is inan overload condition in the case where an amount of data received in areceiving buffer that temporarily holds the received data exceeds athreshold.
 4. The network terminal apparatus according to claim 2,wherein said judgment unit is operable to compare the received data incommunication processing corresponding to a data link layer with thethreshold.
 5. The network terminal apparatus according to claim 2,further comprising a determination unit operable to dynamicallydetermine the threshold depending on a load condition of a process otherthan communication in said network terminal apparatus, wherein saidjudgment unit is operable to judge whether or not the communication isin an overload condition using the determined threshold.
 6. The networkterminal apparatus according to claim 5, wherein said determination unitis operable to determine the threshold depending on a number of runningapplication programs in said network terminal apparatus.
 7. The networkterminal apparatus according to claim 6, wherein said determination unitis operable to determine the threshold depending on (i) the number ofrunning application programs in said network terminal apparatus and (ii)a weight predetermined with respect to each application program.
 8. Thenetwork terminal apparatus according to claim 1, wherein saidcommunication unit includes: a first communication processing unitoperable to execute a communication processing corresponding to aphysical layer and a data link layer; a receiving buffer thattemporarily holds received data from the first communication processingunit; and a second communication processing unit operable to take thereceived data from the receiving buffer and execute communicationprocessing for the received data corresponding to a network layer andthe upper layers, and said judgment unit is operable to judge thecommunication is in an overload condition in the case where an amount ofthe received data held in said receiving buffer exceeds the threshold.9. The network terminal apparatus according to claim 2, wherein saidcommunication unit is operable to execute hierarchical communicationprocessing, and said invalidation unit is operable to prohibit one ofthe interlayer logical connection.
 10. The network terminal apparatusaccording to claim 2, wherein said communication unit includes: a firstcommunication processing unit operable to execute communicationprocessing corresponding to a physical layer and a data link layer; anda second communication processing unit corresponding to a network layerand the upper layers, and said invalidation unit is operable to prohibitsaid first communication processing unit from notifying said secondcommunication processing unit of received data.
 11. The network terminalapparatus according to claim 1, wherein said judgment unit includes: afirst detection unit operable to detect that the communication is in anoverload condition; and a second detection unit operable to detect arecovery from the overload condition, and said network terminalapparatus further comprises a release unit operable to release theinvalidation by said invalidation unit when a recovery from the overloadcondition is detected.
 12. The network terminal apparatus according toclaim 11, wherein said first detection unit is operable to detect thatthe communication is in an overload condition when an amount of datareceived per unit time from the network exceeds a first threshold, andsaid second detection unit is operable to detect a recovery from theoverload condition when an amount of the data received per unit time bysaid communication unit is below a second threshold, after the overloadcondition is detected by the first detecting unit.
 13. The networkterminal apparatus according to claim 12, wherein said communicationunit is operable to execute hierarchical communication processing, andsaid invalidation unit is operable to prohibit one of the interlayerlogical connection.
 14. The network terminal apparatus according toclaim 13, wherein said communication unit includes: a firstcommunication processing unit operable to execute communicationprocessing corresponding to a physical layer and a data link layer; anda second communication processing unit corresponding to a network layerand the upper layers, said first detection unit is operable to judgewhether or not the data received by said first communication processingunit exceeds the first threshold, said invalidation unit is operable toprohibit said first communication processing unit from notifying saidsecond communication processing unit of the received data, and saidsecond detection unit is operable to check whether an amount of datareceived by the first communication processing unit is below the secondthreshold.
 15. The network terminal apparatus according to claim 14,wherein said first communication processing unit is operable to notifysaid second communication processing unit of received data by aninterrupt signal, said invalidation unit is operable to prohibit thenotification by masking the interrupt signal, and said release unit isoperable to release the masking of the interrupt signal.
 16. Acommunication overload avoiding method in a network terminal apparatusincluding a communication unit operable to communicate through anetwork, comprising: judging whether or not communication is in anoverload condition; and invalidating data received by said communicationunit in the case where the judgment is that the communication is in anoverload condition.
 17. The communication overload avoiding methodaccording to claim 16, wherein, in said judging, it is judged that thecommunication is in an overload condition in the case where an amount ofreceived data per unit time from a network exceeds a threshold.
 18. Thecommunication overload avoiding method according to claim 16, wherein,in said judging, it is judged that the communication is in an overloadcondition in the case where an amount of received data in a receivingbuffer that temporarily holds the received data exceeds a threshold. 19.The communication overload avoiding method according to claim 17,wherein, in said judging, the received data in communication processingcorresponding to a data link layer is judged using the threshold. 20.The communication overload avoiding method according to claim 17,further comprising dynamically determining the threshold depending on aload condition of a process other than communication in said networkterminal apparatus, wherein, in said judging, it is judged whether ornot the communication is in an overload condition using the determinedthreshold.
 21. The communication overload avoiding method according toclaim 20, wherein, in said determining, the determined threshold isdetermined depending on a number of running application programs in saidnetwork terminal apparatus.
 22. The communication overload avoidingmethod according to claim 21, wherein said communication unit includes afirst communication processing unit operable to execute communicationprocessing corresponding to a physical layer and a data link layer, areceiving buffer that holds data received from the first communicationprocessing unit temporarily and a second communication processing unitoperable to take the received data from the receiving buffer and executecommunication processing corresponding to a network layer and the upperlayers, and in said judging, it is judged that the communication is inan overload condition in the case where an amount of received data heldin said receiving buffer exceeds the threshold.
 23. The communicationoverload avoiding method according to claim 16, wherein thecommunication unit is operable to execute hierarchical communicationprocessing, and in said invalidating, one of the interlayer logicalconnection is prohibited.
 24. The communication overload avoiding methodaccording to claim 16, wherein said communication unit includes: a firstcommunication processing unit operable to execute communicationprocessing corresponding to a physical layer and a data link layer; anda second communication processing unit corresponding to a network layerand the upper layers, and in said invalidating, said first communicationprocessing unit is prohibited from notifying said second communicationprocessing unit of received data.
 25. A program for avoiding acommunication overload in a network terminal apparatus including acommunication unit that communicates through a network, said programcausing a computer in the network terminal apparatus to execute: judgingwhether or not communication is in an overload condition; andinvalidating data received by said communication unit in the case wherethe judgment is that condition is overloaded.